Electronic musical instrument



June 24, 1952 M. DAVIS ELECTRONIC MUSICAL INSTRUMENT 9 SheetsSheet 1 Filed June 6. 1947 S V A 0D 7 G M 4 GT NW NI YU II M LR m E MC C M C A FIG I SWEEP LIMIT CONTROL WW R T F A F Um u NC P E M T T A A June 24, 1952 M. DAVIS 2,601,265

ELECTRONIC MUSICAL INSTRUMENT Filed June s, 1947 9 Sheets-Sheet 2 WV WWW w s 2A "WWWWNWW FIG 3 l N VEN TOR.

9 Sheets-Sheet 55 FIG 5e M. DAVIS ELECTRONIC MUSICAL INSTRUMENT sweep CIRCUIT HORIZONTAL TIME SWEEP CIRCUIT June 24, 1952 Filed June 6. 1947 VERTICAL INVENTOR MERLIN pAvls PULSE INTEGRA AMPLIFIER /l36 Li I37 m m w COUPLING/I28 June 24, 1952 DAVIS ELECTRONIC MUSICAL INSTRUMENT Filed June 6. 1947 9 Sheets-Sheet 4 lllllll ||L.l llllll-IIIL n mm FIG6 mVENTbR. MERLIN DAVlS June 24, 1952 M. DAVIS ELECTRONIC MUSICAL INSTRUMENT 9 Sheets-Sheet 5 Filed June 6, 1947 Nun mun vNn 4 8 mom m m N3 mam INVENTOR MERLIN DAV! S EPEKQMFE mm 5m OF L 9 Sheets-Sheet 6 iwwu INVENTOR MERLIN DAVIS 1. RN EN M. DAVIS ELECTRONIC MUSICAL INSTRUMENT l wOn June 24, 1952 Filed June 6. 1947 June 24, 1952 M. DAVIS 2,601,265

ELECTRONIC MUSICAL INSTRUMENT Filed June 6. 1947 9 Sheets-Sheet 7 AMPLIFIER PULSE INTEGRATOI? INVENTOR MERLIN DAVIS June 24, 1952 DAVls 2,601,265

ELECTRONIC MUSICAL INSTRUMENT Filed June 6. 1947 9 Sheets-Sheet 8 HARMONIC COMPENSATION AND 49o ATTENUATION 49s If PULSE 492g U INTEGRATOR DETECTOR 244 AMPLIFIER MM PEAKER 509 I HORIZONTAL VERTICAL SWEEP sweep RADIAL CIRCU'T sAw TOOTH UIQIII OIIIII 508- -no as 505 *1- 50s |r 502 SINE WAVE OSCILLATOR DISTRIBUTOR 5o| FREQUENCY CONTROL 00 INVENTOR MERLIN DAVIS Patented June 24, 1952 UNITED STATES PATENT OFFICE (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757) 12 Claims.

The invention described herein may be manufactured and used by or for the Government of the United States for governmental purposes without the payment to me of any royalty thereon in accordance with the provisions of the act of April 30, 1928 (Ch. 460, 45 Stat. L. 467).

This invention relates to an electronic musical instrument and more specifically to an electronic instrument for the production of complex sounds.

Each individual musical note has pitch, quality, and intensity. The pitch is determined by itsfrequency or by the number of vibrations per second it causes in the air. This characteristic determines whether a note is high or low. The quality of the note depends upon whether it is heard as a pure sine wave containing only one frequency or whether it is a compound wave containing a dominant fundamental frequency along with one or more harmonics or multiples of the fundamental. Quality is the characteristic which allows distinction between notes of the same pitch produced by different instruments. Intensity is a measure of the amplitude of the sound wave and is the characteristic which determines loudness. Control of the intensity of a note or of any part of a rendition is known as dynamic control.

Musical notes as sounded by instruments also have a distinguishing characteristic in the variation of intensity with respect to the time of duration of the note. In some instruments such as the organ each note is of substantially uniform intensity as long as the keyboard lever is held down. In other instruments, such as those in which a string is struck or plucked, the intensity may with more or less rapidity build up to a maximum and die away with more or less slowness. The increase of volume during the initial part of the note is known as the attack and the decrease in intensity as the note dies away is known as the decay." This characteristic also provides a distinction between notes of the samepitch of different instruments.

Some instruments such as the piano and organ permit the sounding of a plurality of notes simultaneously to produce harmony. Two or more notes thus played at once produce a chord. If the ratio between thefrequencies of the notes in a chord has a low value, beat notes of slow frequency are produced and such chords are pleasing to the ear and are said to be consonant. However, if the beat notes produced have a relatively high frequency the sound is displeasing to the ear and the chord is said to be dissonant.

The diatonic scale used in modern music has eight notes or steps in an octave, if the last note, one octave higher than the first note, is counted. The octave appears to the ear as a truly natural interval, a note being of twice the frequency of a note an octave lower. In the diatonic scale the intervals between notes have been selected to obtain the maximum of consonance when the notes are sounded simultaneously in chords. The succession of intervals between notes in the diatonic succession is as follows: tone-tone semitonetonetone-tonesemitone.

The modes or arrangements of succession of the diatonic scale as used today are the major and minor. In the major mode the arrangement is as given above. In one minor mode the same succession of intervals is arranged as follows: tone-semitone-tone-tonesemitone tone-- tone.

In the application of the diatonic scale it is natural to select the lowest note of which the scale is composed as the key-note. In music the key-note is invested with special significance making the other six subservient to it. In the scale of C major the lowest note is C and the arrangement of intervals up the scale must be as outlined above for the major mode. Music is written with 12 different keynotes and, because the diatonic scale intervals are more or less incommensurate, it is found that each of these keys requires a different keyboard on a musical instrument for exact intonation.

To avoid either twelve keyboards or fifty keyboard levers per octave as would be necessary to accurately render music in both modes and in the various keys, a compromise is customarily made in musical instruments by providing in each octave twelve notes the spaces between which are equally proportioned. Such an arrangement is known as equal temperament and provides a close approximation for each of the keys. The scale having 12 notes per octave, the notes being approximately a half-tone apart is known as the chromatic scale. This arrangement does not allow accurate rendition of each key since the sharp of one note is not, as so often supposed, the same as the flat of the note following. An instrument arranged for accurate tonal rendition of a key is said to have just temperament.

It is an object of this invention to produce a musical instrument in which a plurality of differently pitched notes may be produced successively by a single means for producing oscillations.

It is also an object to provide a musical instrument in which a complex sound may be produced appearing to the car as a chord composed of several notes of different pitch being sounded simultaneously, said complex sound being produced by a single means for producing oscillations.

It is also an object to provide a musical instrument in which a single keyboard in cooperation with a single oscillation producing means will produce a chord appearing to the ear to consist 3 of thirteen notes of the chromatic scale sounded simultaneously, two of which notes are separated by an octave.

It is also an object to provide a musical instrument which may be simply adjusted to play either in just or equal temperament.

It is also an object to provide a musical instrument which may be simply and selectively adjusted to play in any of a plurality of modes and in any of a plurality of keys so that the keyboard may always be manipulated in one desired key while the music is produced in a key corresponding to the adjustment.

It is also an object of this invention to provide a musical instrument wherein the quality of the notes produced may be generally adjusted.

It is also an object to provide a musical instrument wherein the quality of each note may be separately adjusted to vary with respect to time of duration of the note.

It is also an object to provide a musical instrument in which the intensity of each note may be controlled by the pressure exerted on the corresponding keyboard lever.

It is also an object of this invention to provide a musical instrument in which the intensity of each note may be varied in predetermined manner with respect to the time of duration of said note.

It is also an object of this invention to provide a musical instrument in which a main keyboard representing the notes of the chromatic scale is provided with a supplementary keyboard whereby operation of a key on said supplementary keyboard will sound a corresponding note and simultaneously a note one octave higher or lower.

Other objects will become apparent from the following description taken in connection with the drawings in which:

Fig. l is a schematic diagram of one embodiment of this invention.

Fig. 2 shows a 2-manual keyboard to be used with this invention.

Fig. 2a shows a detail of part of the tremolo producing means.

Fig. 3 is a detailed cross-sectional perspective view of one keyboard manual.

Fig. 4 is a simplified block diagram of one embodiment of this invention.

Figs. 5a-5f are curves used in explaining the operation of Fig. 4.

Fig. 6 is a schematic diagram of one embodiment of this invention.

Fig. 7 is a schematic diagram showing one system of dynamic control that may be used with this invention.

Fig. 8 is a schematic diagram showing a portion of the volume control used with this invention.

Fig. 9 is a schematic diagram showing one system of quality control that may be used with this invention.

Fig. 10 is a schematic diagram of an alternative system of quality control.

Fig. 11 is an alternative electronic distributor device that may be used with this invention.

Fig. 12 is a block diagram of an embodiment of this invention using concentric wave patterns.

Fig. 13 is an elevation view of the wave patterns used in the embodiment of Fig. 12.

Fig. 14 is a partial block diagram showing an embodiment of this invention using cylindrical wave patterns.

Fig. 15 is a partial block diagram showing other elements of the system of Fig. 14.

Fig. 16 is a block diagram of an embodiment of this invention using complementary wave patterns connected in push-pull relation.

Fig. 17 is an elevation view of the push-pull patterns used in the system of Fig. 16.

Fig. 18 is a sectional side view of the patterns shown in Fig. 17.

Reference is now made more particularly to Fig. l of the drawing in which cathode ray tube 30 has an electron gun 31 for producing an electron beam. Tube 30 is so arranged that the beam has the shape of a ribbon having a comparatively long vertical dimension and a short horizontal dimension, the cross section of the beam as it impinges on the end wall 32 being substantially a line as shown at 33, Deflecting plates 34 are provided for deflecting said beam horizontally. End wall 32 carries a plurality of patterns 36, 31, and 38 which may vary sinusoidally in form and which may be made of metal foil. The uppermost pattern 36 consists of one complete sine wave. The second pattern 31 while of substantially the same length as pattern 36, consists of two sine waves. Pattern 38 which is of the same length consists of three sine waves. It will thus be seen that pattern 31 represents a wave which is the second harmonic of wave 36 while pattern 38 represents a wave which is the third harmonic of pattern 36. Patterns 36, 31, and 38 are connected through attenuator circuits 40, which are controlled by stops 4|, and through amplifier 42 which is in turn connected to speaker 43. Attenuator circuit 40 is constructed to selectively attenuate the signals picked up by patterns 36-38 as will be disclosed in greater detail below.

Electrode 44, also carried by end wall 32 of tube 30, is located in alignment with one end of the patterns 36-38. Electrode 44 is connected through conductor 45 to sweep-limit control circuit 46. A circuit suitable as a sweep limit control circuit will be described in detail with respect to Fig. 6. Deflecting plates 34 are connected through clamping circuit 41 and amplifying circuit 48 to saw-tooth oscillator circuit 50.

Saw-tooth oscillator circuit 58 comprises a condenser 51 connected in parallel with a gas-filled triode 52. The cathode of vacuum tube 52 is connected to ground. The grid of tube 52 is connected to ground through a biasing battery 53, and is inductively coupled through coils 55 and 56 to sweep-limit control circuit 46. The plate of tube 52 is connected through frequency control pentode 68 to plus battery and through the battery to ground completing the circuit for charging condenser 5| through pentode 60. Condenser 5| is discharged through triode 52. The cathode of tube 60 is connected to the plate of tube 52 and the plate of tube 60 is connected to plus battery.

A keyboard 65 is provided along with a supplementary keyboard 66. Keyboard 65 comprises the usual black and white levers of the piano or organ as will be described in greater detail below. Keyboard 66 consists of very short levers, one corresponding to each of the black and white levers on keyboard 65, each keyboard lever in keyboard 66 being directly in front of and closely adjacent to the corresponding lever in keyboard 65. Each lever in keyboard 65 and 66 is provided with a contact shown at 61. In their normal unoperated position, these contacts engage one end of resistors 68 or 68' shown on the right side of the contacts 61. When the levers are pressed, contacts 61 engage one end of resistors 63 or 69' shown on the left side of contacts 61.

The other ends of resistors 68 and 69 are connected together and through battery 12 to the cathode 13 of cathode ray tube 15.

Thirteen electrodes such as shown at 8l-93 are fixed to the end wall of tube 15. Tube 15 is also provided with deflecting plates 16 and 11 for deflecting the cathode ray beam in mutually perpendicular directions, the cathode ray beam being produced by electron gun 18. Deflecting plates 16 and 11 are supplied by sweep circuits 14 with sine waves 90 degrees out of phase so that the electron beam is swept in a continuous circle over electrodes 8l-93 at a super-audible speed. Twelve of these electrodes 8|93 are each connected to one of the contacts 61 in each octave of the normal keyboard 65 through conductors such as 95 and 96. The thirteenth electrode 93 is connected to contacts 61 of the supplementary keyboard 66.

One keyboard lever 19 of keyboard 66 has associated therewith resistors 68 and 69 corresponding to resistors 66 and 69 of keyboard 65. Keyboard lever 19 controls a contact 61 which engages one end of resistor 68' when the lever is unoperated and one end of resistor 69" when the lever is pressed. However, the other levers of keyboard 66 have associated therewith a contact 1| which is connected to the end of said resistor 68 which engages contact 61 associated with lever 19. The other ends of resistors 68, 68, 69 and 69' are connected to battery 12 and also to the cathode of pentode 69. The contacts such as 1| in connection with keyboard 66 may be used in place of the plurality of resistors 68' as shown in connection with keyboard 65 because only one lever of keyboard 66 is ever depressed at one time whereas a plurality of levers on keyboard 65 are operated simultaneously therefore one silent resistor will serve the entire keyboard 66.

Resistors 68, 68', 69 and 69 are successively connected in a circuit including battery 12, the electron beam of tube 15 and one of contacts 8l-93. Connections are made from the other ends of resistors 68 and 68 and selected points on resistors 69 and 69' to the grid of tube 69. Resistors 68, 68, 69 and 69' therefore form parts of potentiometers and the voltage picked up across resistors 68 and 68' is sufficient to prevent tube 69 from passing current while the voltage picked up from the intermediate taps of resistors 69 and 69 causes tube 69 to pass current commensurate with the tone of the keyboard lever pressed.

The selected points of resistors 69 mentioned above are shifted slightly along said resistors through the action of switches 91. There is one switch 91 provided for each resistor 69. Switches 91are ganged for group action and are operated by a single operating handle or stop 98 marked just-equal. Switches 91 are effective to connect either of two selected points to the grid of tube 69. Changing the point at which a resistor 69 is connected to the grid of tube 69 obviously will change the pitch sounded by the associated keyboard lever. The points on resistor 69 tapped by switches 91 are so selected that with stop 98 in one position th instrument will play in just temperament and with the stop 98 in the other position the instrument will play in equal temperament. Switches, not shown, similar to switches 91 should be provided for resistors 69' of keyboard 66.

In just temperament a change in the key note from one note to the next higher note means that the pitch of all the notes is raised by being multiplied by the pitch ratio of said two key notes. In just temperament this pitch ratio between adjacent notes will not be the same for every two adjacent notes. In equal temperament a change from one key note to the next higher key note means that the pitch of all notes is raised by being multiplied by 1.059, a number such that its product and succeeding products will divide an octave into twelve equal intervals. In equal temperament since all the notes are raised by one factor when the key note is changed the key signature stop may operate one set of switches adjusting the resistance of one resistor in the connection between cathode 13 of distributor 15 and keyboard 65 and 66.

In operation, when levers of keyboard 65 are unoperated the contacts 61 engage resistors 68 but when the levers are depressed the contacts 61 engage resistors 69. Current flows from battery 12 through one or the other of resistors 68 or 69 thence through whichever one of the electrodes 8| to 93 on which the beam generated by electron gun 18 is impinging, and back to battery 12. Resistors 68 and 69 thus operate as potentiometers and a voltage will be applied through line 89 to the control grid of pentode 69, said voltage being determined by the position of the intermediate tap of the resistor 69 or the voltage across resistor 68 which are associated with the lever pressed. Supplementary keyboard 66 operates in a similar manner current passing through electrode 93 and through whichever resistor 69' that corresponds to the lever pressed. However, when a lever is pressed on keyboard 66 the corresponding lever is also operated in keyboard 65 because of a mechanical linkage, to be described more in detail later, between the levers of keyboard 66 and 65. This arrangement allows two notes one octave apart in pitch to be sounded simultaneously on one keyboard.

Various voltages are thus applied in quick succession to the control grid of tube 69, these voltages corresponding in magnitude to the pitch represented by the levers pressed on keyboards 65 and 66. The current through tube 69 varies in accordance with the voltage on its control grid and charges condenser 5| at varying rates of speed. Condenser 5| is discharged by triode 52. Upon actuation by the impinging of the electron beam in tube 39 on electrode 44 sweep-limit control circuit 46 applies a pulse to the grid of triode 52 through inductively coupled coil 55-56 to cause tube 52 to conduct. This causes condenser 5| to discharge as trace 33 completes its sweep over patterns 36-38 and causes trace 33 to return to the beginning of its sweep.

The voltage to which condenser 5| is charged is amplified by circuit 48 and converted into two oppositely swinging voltages each of which swings in a direction opposite to the other and at a rate in accordance with the charging rate of condenser 5|. These oppositely swinging voltages are applied to clamping circuit 41 which fixes the upper limit of the swing of each of the voltages and applies them to the deflecting plates 34 of tube 39 to limit the travel within the bounds of the patterns on the side opposite electrode 44.

This causes the ribbon beam of tube 39 to swing back and forth across patterns 36, 31 and 38, At any instant more or less current will flow from patterns 36-38 in accordance with the area of said patterns that is being impinged upon at that instant by the electron beam. Thus it will be seen that the current will flow representing the fundamental in accordance with pattern 36 andalso the harmonics represented by patterns 31 and 38. The current picked up by patterns 36-38 is attenuated in circuits 40, as controlled by stops 4|, is amplified in circuit 42 and repro duced'audibly by speaker 43. 1, .If:no.levers; on keyboards 65 or are pressed the control'grid of tube 60 is so biased that condenser I is not being charged. Hence, the ribbonibeam in tube 30 is not deflected; A steady current .will be passedon .to.circuit 40 and no vibrations will be audibly reproduced by speaker 43. It will be obvious that the sound could also be extinguished by blocking: the beam incathode ray. tube 30 andthat the sound could be ,muilied by partially blocking said beam.

' If one lever is pressed onkeyboard 65, on each instantLthat the electron beam ofrtube 75 passes the corresponding electrode of electrodes 8I-93 condenser 5| will be charged at a rate determined by the pitch value of the key pressed. During this instant the ribbon beam in tube 30 will move horizontally along the patterns generating a current. having a fundamental and harmonics at a frequency depending on the pitch value of the lever pressed. A corresponding operation will follow from the pressing of the other levers in keyboard 65.

If two levers are simultaneously pressed on keyboard 65, the pitch of one lever will be sounded as the electron beam in tube impinges on its corresponding electrode of electrodes 8| to 93 while the pitch of the other key will be sounded as its corresponding electrode is impinged upon. The rate of sweep of the electron beam in tube I5 is at a superaudible rate so that the pitches of the two notes are heard in succession during very small increments of time. It will then appear to the ear that the two notes are played simultaneously. It will be evident that all twelve notes in the chromatic scale may be sounded at onetime, the notes being scattered throughout the octaves on the keyboard.

If two notes an octave apart are to be sounded simultaneously then the lever on the supplementary keyboard 66 corresponding to the lower of the two notes, for right hand execution or higher of the two notes for left hand use is pressed. This action automatically presses the lever opposite and corresponding to the upper or lower octave note in keyboard 65 and it is sounded through the action described above. The pitch resistors 69' are arranged so that the levers of keyboard 66 to the right of the center sound a note one octave lower than the opposing lever on keyboard 65 while the levers of keyboard 66 to the left of the center sound a note one octave higher than the opposing lever of keyboard 65. The lever of keyboard 66 which is pressed contacts a resistor 69 and causes a current to flow by impingement of the beam on electrode 93 of tube I5 causing the note an octave higher to be sounded during the thirteenth increment of the sweep-cycle in tube I5.

It is thus seen that, through the operation of a single oscillation producing means 30, a plurality of pitches may be produced in succession and that these pitches can be produced in such rapid succession that they appear to the ear to be simultaneously sounded.

In Fig. 2 is shown the two-manual keyboard arrangement preferably used in this invention. The two main keyboards 65 and 65' are each associated with auxiliary octave keyboards 66 and 66', respectively. The means for producing a tremolo effect are mounted immediately behind 8 the keyboards and will be described in detail below.

The construction of a main keyboard 65 and octave keyboard 66 is shown in Fig. 3. White lever I00 and black lever IOI of keyboard 65 correspond to the black and white levers on the keyboard of a conventional piano. Levers l00' and IOI of octave keyboard 66 are directly in front of corresponding levers I00 and IOI. Lever I00 is provided with a hinge at I02 and maintained in its normal up position by tension spring I03. Lever I00 is provided with a hinge I06 and maintained in its normal up position by adjustable compression spring I0I.- Adjustable dashpots I09 and- H0 provide a proper inertia to the actionof levers I00 and I00, respectively. The other levers of keyboard 65 and 66 are similarly provided with hinges, springs and dashpots, and have a similar construction. Hook member III fixed to lever I00 cooperating with member II2 of lever I06 causes lever I 00 to be. depressed when-octave lever I00 is pressed.

If two notes one octave apart are to be played, the lever of octave keyboard 66 adjacent to the lower note in right hand execution (or adjacent the upper note for left hand execution) on keyboard 65 is pressed. The operating of the octave lever also operates the lever of keyboard 65.- Thus without unduly stretching the fingers, a note, along with a note an octave higher or lower, as required is sounded by operation of one keyboard lever. The electrical contacts necessarily associated with the levers of keyboards 65 and 66 are not shown in Fig. 3.

Referring now more particularly to Fig. 4 for a general description of a modification of this invention, cathode ray tube I I5 is of the type which produces a pencil-like beam of narrow cross-section. Tube II5 includes cathode H6, horizontal deflecting plate I I1, vertical deflecting plates II! and patterns H9 and I20.

Horizontal deflecting plates II? are connected to horizontal sweep circuit I22 which is in turn controlled by keyboard I23. It will be understood that keyboard I 23 and horizontal sweep circuit I22 have associated therewith an octave keyboard and distributor as shown in Fig. 1. Ver-, tical deflecting plates II8 are connected to vertical sweep circuit I24.

Patterns H9 and I are connected through frequency compensator circuit I26 and harmonics attenuator circuit I21, coupling circuit I26 to pulse integrator circuit I29. Circuit I26 contains a pre-set resistor for each of patterns H9 and I20, the resistor attenuating the signal picked up by each pattern to compensate for the selective hearing characteristics of the ear. Circuit In provides for the circuit of each of patterns II! and I20 a potentiometer including a tapered're-, sistance. These potentiometers are selectively operable by stops not shown so that the various harmonics can be suppressed or accentuated in order to simulate different musical instruments or produce new complex sounds.

Coupling circuit I28 gives a direct current coupling between harmonics attenuator I2! and pulse integrator I29. Pulse integrator I29 is a circuit capable of integrating the electrical pulses supplied to itduring each vertical sweep of the electron beam in cathode ray tube II5. Conductor I30 connects vertical sweep circuit I24 with pulse integrator I29 to supply the latter with a tripping pulse at the end of each vertical sweep. Pulse integratorcircuit I29 is connected through detector I and amplifier I36 to speaker 9 I31. Circuits I28, I29, I35 and I36 will be described in greater detail below.

In the operation of the system shown in Fig. 4, the spot trace of the pencil electron beam produced in tube I I sweeps vertically over patterns H9 and I20 at a relatively rapid rate determined by sweep circuit I24. The pencil beam of tube II5 sweeps across patterns II9I20 horizontally at a rate which depends on the lever being operated in keyboard I23 but at a rate which is always slow compared to the vertical sweep rate.

In Fig, 5a there are representations of fundamental pattern I I9 and second harmonic pattern I28 with line I40 representing the trace of spot I40 of the pencil beam. Arrows indicate components of beam travel. Although shown vertical the beam trace would have a slight slope as it proceeds in zigzag fashion across the patterns. The return trace of the beam is ignored because it is so rapid as to produce a negligible signal. If desired the return trace may be blanked out by use of a blankin pulse applied to a control grid in cathode ray tube H5. Fig. 5b shows the signal produced by the patterns II9-I20, ne lecting the effects of frequency discrimination compensator circuit I26 which would govern the relative amplitude of the signals emanating from the patterns in accordance with auditory requirements. In Fig. 5b the unshaded and shaded pulses represent the signal produced by transit of the beam across patterns I I9 and I20 respectively along representative traces I40" shown in Fig. So. It will be obvious that as the beam traverses the patterns in a nearly vertical direction there will be produced by each pattern a pulse having a duration equal to the time during which the beam impinged on the pattern, and since the ver tical deflection rate is uniform, the pulse duration will be a measure of the pattern height at the position of that trace.

Fig. 5c shows the pulses produced by patterns H9 and I20 after attenuation by compensating network I26 and harmonics attenuator I21. In this figure the pulses representing the second harmonic have been appreciably attenuated either to compensate for the selective characteristics of the ear or because of selective suppression of this harmonic to achieve a desired effect, or for both reasons.

Fig. 502 shows the output of pulse integrator I29 in which a condenser is charged as shown in Fig, 5 by the pulses shown in Fig. 50. Fig. 5] shows the condenser charge voltage plotted against time. The higher the voltage of the pulse, the higher will be the charging rate of the condenser, curves CR1-CR4 showing different charging rates. As seen in Fig. 5d, the condenser will be charged at a high rate (angle A) for a high. pulse and at a slow rate (angle B) for a short pulse and will be discharged at the end of each complete vertical sweep through action of tie I 30 between pulse integrator circuit :29 and vertical sweep circuit I24.

Detector I55 detects the pulses produced by integrator circuit I29 and produces a curve such as shown in Fig. 5e, it being understood that in practice there would be a large number of integrated pulses as shown in Fig. 5:1 to give a relatively smooth curve as shown in Fig. 5c. The

speed with which the electron beam in tube II5 wave shown in Fig. 56 which, in turn, determines I the pitch of the note sounded.

Reference is now made to Fig. 6 for a detailed description of an embodiment of this invention operating with a pencil cathode ray beam as generally described with respect to Figs. 4 and 5c5f. Cathode ray tube I includes cathode I5I, control grid I52, horizontal deflecting plates I53, vertical deflecting plates I54 and on its end wall there is a mounting plate I55 carrying patterns I56-I65. Power supply I10 provides voltages to the various electrodes of tube I50 to produce a pencil beam of relatively small cross section.

In Fig. 6 the conductors 95, 96, etc. corresponding to the conductors of like number in Fig. 1

lead to the contacts of the distributor tube through resistors I1I, I12, etc. Resistors HI and I12 are arranged with shorting switches I13 and I14, respectively, arranged to selectively shunt parts of said resistors. Shorting switches I13, I14 are ganged to operate from key signature stops I 15 and I16, each stop operating one shorting switch of each resistor. It will be understood that the wires associated with each keyboard lever each contain a potentiometer like 58, 68', 69, 69 of Fig. 1. The resistors Ill and I12 lead to the contacts I8I of a distributor tube I82. This distributor tube corresponds to distributor tube 15 in Fig. 1. Tube I82, however, is an alternate type being a cylindrical tube having its contacts I8I in cylindrical array and the cathode I83 running axially of the tube. Deflection coils I85, I85, I81 and I88 are fed with an alternating current from source I90. Condenser I9I is connected in series with coil I86 so that a rotating field will be produced about tube I82 and cause a planar sheet of electrons to be emitted from cathode I83 and sweep radially around the tube and across the contacts I8I at a speed determined by the frequency of the source I90.

The anodes I8I of distributor tube I82 may be separated and shielded from each other to prevent the beam from impinging on two anodes at the same time. The resistance of the beam contact as it passes from one anode I8I to the next is so low in comparison to the impedance in series with it that the effect should not be apparent until the beam has almost passed over one anode prior to contact with the next.

The switching speed of the electronic distributor tube I82 of Fig. 6 is limited only by the magnetic properties of the rotary sweep circuit and this may be as high as 10,000 cycles per second which would allow 130,000 switchings per second. Switching from one audible frequency to another is performed at a supersonic rate.

Resistors such as HI and I12 appearing in the potentiometer circuit associated with each keyboard lever will obviously affect the current passing through these potentiometer circuits in accordance with the amount of the resistances HI, I 12, etc. that are shorted out by the key signature stops such as I15 and I16. This amount of shorting in turn will affect the voltage applied to the grid of tube 69 through conductor 19 and thus affect the pitch of the note sounded. Snorting switches such as those designated as 113 are positioned along resistor I1I so that operation of one key signature stop such as I15 operating to close one shorting switch in each resistor I1 I, I12, etc. will cause the notes sounded by keyboards and 66 to be in any one of the various keys and modes represented by stops I15 and I16. Other stops arranged in equal manner may be employed to provide alternate potentiometer taps to cause the instrument to play in equal or just temperament and in the various modes.

The switches such as I13 may be arranged so that the over-all pitch lever is raised by the resistors such as I'II until the base frequency or pitch sounded by the white keyboard lever normally producing C-natural is equal to that of the key note represented by the signature. The white keys which normally represent the scale at the key of C now will represent the scale in the key selected. The signature written on the music will remain as usual but the musical notation will need to be transposed to the key of C. In this system, except for transposing incidentals, all music will be played on the white keyboard levers and the given note position on the staff will always'be represented by the same keyboard lever. Each keyboard lever will therefore sound a different pitch depending upon the key selected in contrast with piano operation in which each keyboard lever always sounds the same pitch. If the scale pitches are selected in the just tempered scale then true harmony will result. Adjustment from equal to just temperamentor vice versa is affected by gang selector switches operating on the pitch potentiometer such as switches 91 in Fig. 1. In order to play in the various minor as well as the major modes from 12 to 26 key signature change switches will be required. Since the minor mode scale step arrangement differs from the major mode, additional gang selector switches such as I73 in Fig. 6' operating on the pitch potential circuit will be required. The black keyboard levers would then be arranged to represent intermediate frequencies between key scale steps for modulation purposes. These might have equal tempered values or just temperament attuning to selected transposition keys.

Alternatively, the switches such as H3 in Fig. 6 may be arranged so that music written in keys other than the key of C (i. e. written in sharps or flats) may be played on the keyboard as though written in the key of C. In this system the musical notation would be used unmodified. The keyboard would be played as usual except that the key signature flats and sharps would be disregarded and executed as though natural. The shift of the white keys to the proper sharps and flats would be done by depressing key signature switches such as I13 in Fig. 6. In this system all of the notes are not shifted by a certain ratio but the various notes are changed in pitch each by its required amount.

Wire 79 from keyboards 65 and 66 is connected with the control grid of pentode 60. The cathode of pentode 60 .is connected to conductor 80 from keyboards 65 and 66. Frequency control tube 60 is connected to saw-tooth oscillator circuit 50 as explained with respect to Fig. 1. The output of saw-tooth oscillator circuit 50 is fed to paraphase amplifier circuit 48 containingtriodes I95 and I96. The plate of gas-filled tube 52 is connected through condenser I 91 to the grid of tube I95. The junction of condenser I91 and the grid of tube I95 is connected through resistors I98 and I99 to the cathodes of tubes I95 and I96. The junction of resistors I90 and I99 is connected to the grid of tube I96.

The particular form of paraphase amplifier employed in circuit 48 employs coupling between the cathodes of the two tubes I95 and I96. Current from both tubes fiows through the common cathode resistor I99. Grid voltage on tube I95 is the voltage developed across cathode resistor I99 and is of opposite sense to that directly on the grid of the amplifying tube I95. The output of triode I96 is thus inverted with respect to the output of tube I95. The plates of, triodes I and I96 are each connected through a separate resistor to a common source of plus potential. The outputs of paraphase amplifier 48, two mutually inverted saw-tooth waves, are fed to clamping circuit 41.

Clamping circuit 41 comprises diodes 200 and 20I. The output of triode I95 is connected to the cathode of tube 20I and also to one of the horizontal deflecting plates I53 of cathode ray tube I50. The output of triode I96 is connected to the plate of diode 200 and also to the other of deflecting plates I 53. The plate of diode MI is connected to ground while the cathode of diode 200 is connected to an adjustable biasing source of potential. It will be obvious that diodes 200 and 20I will conduct in opposite directions when the mutually inverted deflection voltages attain sufficient amplitude. Thisresults in clamping one extreme of each opposed sawtoothed horizontal deflecting voltage at one point and causes one side of the sweep of the electron beam to remain always fixed regardless of amplitude variations.

The vertical deflection voltage is initiated in saw-tooth oscillator 205, a vacuum tube oscillator capable of generating a frequency of 100,000 cycles per second or more. Oscillator circuit 205 of triode 206 is maintained above ground by cathode resistor 208. The grid of tube 206 can be made highly negative with respect to its cathode since it is dependent upon the current through pentode 201. The current through pentode 20'! may be regulated by adjustment of its screen grid voltage through manipulation of potentiometer 209. Triode 206 will be non-conducting while condenser 2II is being charged from source of plus potential 2I2. As condenser 2| I becomes charged triode 206 becomes conducting regardless of the highly negative grid. This results in plate current through resistor 2I3. The grid of pentode 201 is thereby affected through condenser 2I4 and resistor 2I5. The grid of pentode 201 then goes negative and current decreases through pentode 201. Because of the grid connection of triode 206 with plate resistor 2I6 triode 206 becomes more conducting and finally positive. Condenser 2II discharges very quickly through this tube. When voltage across condenser 2 I I decreases enough the grid of triode 206 gains control and the cycle repeats.

The output of oscillation generator 205, a sawtooth wave, is fed to the input of paraphase amplifier 220 through the primary of transformer 22I. The secondary of transformer 22I operates to trip the pulse integrator in a manner to be described later. Paraphase amplifier 220 has a construction and operation similar to that already described for paraphase amplifier 48. The output from paraphase amplifier 220 is connected through clamping circuit 222 to vertical deflecting plates I54 of cathode ray tube I50. The construction and operation of clamping circuit 222 is similar to that described above with respect to clamping circuit 41,

In tube I50 each of patterns I56 to I65 are connected through frequency compensating resistors such as 225 to tapered-harmonic-attenuator resistors such as 226. Resistor 226 forms part of the potentiometer circuit going back to voltage supply I10. The adjustable tap along each logarithmically tapered resistor 226 feeds through a resistor 22'! to the cathode of diode 230 and the plate of diode 231 in positive coupling circuit 233.

Frequency compensating resistors 225 correspond to the resistors in circuit I26 of Fig. 4 while the tapered potentiometers, such as 226, correspond to those in the circuit I21 of Fig. 4. The function and purpose of circuits I26 and I21 has already been explained with respect to Fig. 4. Since the voltages from potentiometers such as 226 must be combined before being amplified for the speakers, high series resistors such as 221 must be added in the voltage tap line of each potentiometer 226 to prevent short-circuiting when these lines are connected to a common lead. A switch such as 232 is shown between each resistor 225 and potentiometer 226 is provided whereby each anode I56 may be grounded when not used in order to prevent the anodes from accumulating a charge when disconnected.

The purpose of the positive coupling stage 233 is to assure that the coupling condenser 234 used to block potentiometer voltage from the grid of the pentode 236 in pulse integrator circuit 231 is not rendered insensitive to the incoming pulses by accumulation of charge, and to insure that the pulsations are transmitted with their full intensity. Incoming pulses are prevented from shorting to ground by the rectifying action of diode 23I while passing unimpeded through diode 230. The voltage drop across grid resistor 230 supplies the signal pulse passed on to pulse integrator circuit 231. In this process a small charge accumulates on condenser 234. During the period following the pulse the condenser becomes neutralized by a flow of current through the rounded diode 23I. This current flow has no action on the stage 231 since the direction of this current is opposed by the other diode. The original signals are thereby transmitted through the coupling circuit 232, without alteration by said circuit, as unidirectional pulses to the pulse integrator stage 231.

Pulse integrator stage 231 includes pentode 236 and triode 240. The output of coupling circuit 233 is applied to the grid of pentode 236 in pulse integrator circuit 231. Circuit 231 also includes condenser 24I charged by battery 242 through resistor 243 and pentode 236. Resistor 243 is the cathode resistor of vacuum triode 240, the grid of which is connected through conductor 244, differentiator circuit 246, and conductors 241 to" the secondary of transformer 22I in the input of amplifier 220. A by-pass condenser is provided across cathode resistor 243. One side of condenser 24I is connected to the cathode of triode 240. The other side of condenser 24I i connected to the plate of triode 240. The output of integrator circuit 231 is taken from the positive side of condenser 24 I.

In operation, each pulse, such as those shown in Fig. c, impressed on the grid of pentode'236 causes that tube to pass a pulse of current from battery 242 to condenser 24I. Current from battery 242 flowing through cathode resistor 243 causes triode 240 to be normally non-conducting with a grid bias Eg (Fig. 5)) within the substantially linear portions of condenser 24I charging curves. However, the high rate of change of the! vertical deflection voltage during the return stroke of the electron beam in tube I50 causes a pulse, of relatively large magnitude to be induced in the secondary of transformer 22l and timed to dis-i charge condenser 24I before the voltage has reached the cut off voltage Eg. This pulse is properly shaped by differentiator circuit 246 and applied to trip tube 240, making that tube conducting and discharging condenser 24I. Diiferentiating circuit 246 consists of a condenser and resistor in series forming a circuit having a time constant about one-tenth that of the vertical oscillation cycle applied to plates I54 of tube I50. The effect of integrator circuit 231 is as described with respect to the integrator circuit in Fig. 4 and with respect to Fig. 5d.

The output of pulse integrator circuit 231, which is the charge on condenser 24I, is applied to the input of detector circuit 244, being connected to the plate of diode 246 and the cathode of diode 241. A resistor 249 and condenser 248, connected in parallel are connected between the cathode of diode 245 and the plate of diode 241. Detector circuit 244 operates in a manner similar to that of coupling circuit 233 in that is preserves the direct current component of the signal. However, condenser 248 is charged by each pulse, such as shown in Fig. 5d, in the output of the integrator circuit and discharged through resistor 249 between pulses. The output of circuit 244 taken from across condenser 248 is, therefore, the envelope of the input pulses as shown in Fig. 5e.

The output of detector circuit 244 is taken from acros condenser 248 and applied across tapered resistor 252 in volume control circuit 253. Condenser 250 in series with resistor 25I tapped to the lower end of resistor 252 provides overall frequency compensation. A tap adjustable along resistor 252 applies the output of volume control circuit 253 to the control grid of pentode 256 which acts as a driver tube to push-pull ampliher 200. Resistor 252 is logarithmically tapered to compensate for the logarithmic sensitivity of the car so that equal adjustments of the intermediate tap will produce equal changes in volume.

The output of amplifier circuit 260 is impressed on the input of speaker divider circuit 210 where it is divided into high frequencies, which are impressed on high frequency speaker 216, and low frequencies which are impressed on low frequency speaker 211. The high and low frequencies are separately made audible to obtain better sound efiect.

Sweep limit control circuit 46 contains triode 54, the grid of which is connected to the junction of resistor 51 and the plus side of power supply I10. When the electron beam of tube I50 impinges on electrode 44, a current flows through said beam, electrode 44, resistor 51 and power supply I10 to the cathode I5I of tube I50. This momentary flow of current through resistor 51 causes a pulse to be applied to the grid of triode 54. The amplified. pulse is passed through transformer 58 to trip gas filled triode 52, as explained above. and cause the return of the electron beam in tube I553 to the starting place along the horizontal axis. The electrode 44 is the same as that shown. in tube I I5 of Fig. 4.

Time beat emphasis circuit 200 receives spaced s u are waves from generator 28 I and applies them to control grid I52 of tube I50. Generator 28I develops square pulses of adjustable amplitude duration and spacing. The pulses applied by circuit 2% to grid I52 momentarily change the intensitv of the electron beam of tube I50 and cause the music rendered to have accentuated olume or beats at regular intervals. This may be arranged to give automatic accent to the notes at the end of each measure so that the rhythm of the music may easily be held constant.

The electron beam in tube I50 may also be varied in intensity to control the attack-decay volume of each note as will be described below with respect to Fig. '1.

Reference is now made more particularly to Fig. '1 for a description of some of the volume or dynamic controls used in this invention. In Fig.7 is seen distributor tube I82, battery 12, pitch resistors 69, and key signature resistors I13I14 substantially as seen in Figs. 1 and 6. Fig. 7, however, shows a modification of the pitchpotentiometer circuit in that there are no silent resistors 68, the pentode 60 being so biased that, with no bias applied to its control grid, it will not conduct and no charge will be fed to condenser 5I. Pentode 60 is connected to the taps of the various pitch potentiometers 69 by the pitch contacts such as contact 300 of keyboard lever 30I.

The above described potentiometer circuit for selective pitch control is an additional modification in that the contacts 300 and 300' break the various potential lines to the grid of the pentode tube 80 rather than the current in the various parallel potentiometer circuits. It will be understood that there is a contact such as 300 and 300 for each lever on the main keyboard and that each of such contacts is associated with a lever such as 30I.

In Fig. '1 the pitch potentiometer circuit associated with keyboard lever 30I includes the electron beam and a contact I8I of distributor tube I82, battery 12, pitch resistor 69 and key-signature resistor I13. In parallel with this circuit are one or more dynamic control circuits including the electron beam and a contact I8I of distributor tube I82, battery 12, attack-decay potentiometer 304 and resistors 305. Since each of thes parallel circuits have high impedances, current drain in one circuit does not materially affect the other.

I The attack-decay potentiometer 304 includes a tapered ring-like resistor 308, the inner surface of which is circular and engaged by rotating contactor 301. Contactor 301 is fixed to shaft 308 of motor 309. Shaft 308 is normally prevented from rotating by arm 3I2 fixed thereto which normally abuts against arresting member 3 carried by bar 3I5. Bar 3I5 is slidably mounted in supports SH and 3I8 and carries arresting member 320 capable of arresting arm 3I2 after it has rotated 180 degrees from member 3. Bar 3I5 is moved in an axial direction by solenoid 322 and is biased by spring 32I so that arm 3I2 normally abuts against arresting member 3I4.

When solenoid 322 is energized, bar 3I5 is moved against the tension of spring 32I; arresting member 3I4 is moved from under arm 3I2 and shaft 308 starts to rotate carrying with it contact 301. With the moving of bar 3 I 5 arresting member 320 has now moved in the way of arm 3I2 and arrests arm 3I2 after it has rotated I80 degrees. When solenoid 322 is deenergized, bar 3 I 5 moves to its normal position, arresting member 320 is moved from over arm 3 I2 and shaft 308 and contact 301 rotate another 180 degrees till arm 3I2 is again arrested by member 3I4. Solenoid 322 is connected in series with battery 334, adjustable resistor 335, and contact 338 associated with keyboard lever 30I. Operation of lever 30I therefore energizes solenoid 322 subsequent to closure of pitch contacts 300.

Shaft 308 also has fixed thereto a conducting disc 323 straddled by the poles of electro-magnet 324 having winding 325. Winding 325 is connected in series with battery 326 and adjustable resistor 321. Resistor 321 is adjustable through movement of contactor 328 which is controlled by foot pedal 329. It will thus be seen that the speed of rotation of shaft 308 and contact 301 is controlled by the position of foot-pedal 329.

Also connected in the dynamic potentiometer circuit are series resistors 305, each of which is shunted when a corresponding contact spring 338 makes contact with bar 339. The face of bar 339 engaging springs 338 is tapered so that the springs are engaged in succession. Bar 339 is fixed to keyboard lever 30I and when lever 30I is depressed, bar 339 is raised to successively contact springs 338 and shunt resistors 305 successively out of the dynamic potentiometer circuit, allowing increasing amounts of current to flow in that circuit. Resistor 305 similar in construction to resistor 305 but associated with a different keyboard lever is shown schematically. It will be understood that each of these resistors or parallel ones extending from lines 303 are also operative keyboard levers which are octaves of this note on the main keyboard.

Dynamic potentiometer 304 is shown schematically. Potentiometer 304 is similar in construction to potentiometer 304 but is associated with a different distributor contact I8I and its associated keyboard levers, representing one note and its octaves on the main keyboard. Potentiometer 304' has contact 301', arm 3I2, and stops 3I4 and 320' corresponding to elements 301, 3I2, 3| 4 and 320 of potentiometer 304.

Contact 301 of potentiometer 304 is connected through shaft 308 which has ends of insulating material and contact 342 to the contacts of the other corresponding potentiometers, such as contact 301' of potentiometer 304' and selector switch 348 to the cathode of triode 350, the plate of which is connected to the control grid of cathode ray tube I 50 which contains the sine-wave patterns as seen in Fig. 6. Details of the selector switch stop mechanism will be described later under Fig. 9. There will be thirteen attack-decay potentiometers, such as potentiometers 304304', one for each contact I BI of distributor tube I82, to give one attack-decay characteristic.

Other sets of such dynamic potentiometers not shown having different attack-decay characteristics may be provided and any set may be selected by means of switches 348. One stop of switch 348 might bring into operation a set of potentiometers giving the attack-decay characteristics of a piano while another stop might give the attack-decay characteristics of a banjo. The other stops similarly represent other attack-decay characteristics. Each set of attack-decay potentiometers operated by one stop of switch 340 contains one potentiometer such as potentiometers 304 and 304' for each contact I8I of distributor tube I82. The volume resistors such as 385 of each keyboard lever ar connected in parallel with each of the associated attack-decay potentiometers. Such a connection is indicated by wires 303. The potentiometers of each attack-decay set are connected to a corresponding contact |0I of distributor tube I82. Such connections are shown at 3 I0.

In operation of the circuit shown in Fig. '1, when keyboard lever 30I i pressed, contact 300 is made connecting the grid of pentode with the pitch potentiometer corresponding to lever 30I and causing a not to be sounded by loudspeakers 216211 (see Fig. 6) said note having a pitch corresponding to lever 30I as explained above. As lever 30I is depressed further, contact 336 is closed energizing solenoid: 3221 and.

causing contact 30.?!- of potentiometer 304. torotate l 80. degrees atia, speed: controlled bythe position. of: foot pedal 32.8. As the varying voltage pickedupby contact is applied-to the grid of triode 350 to control the intensity of the beam in tube I50, the volume of the note sounded increases at. a. speed determined. by pedal. 32.9. a

according to a law. determined by. the taper. of

resistor 306. to provide the attackdesired.v

As long. as keyboard lever 30,! is held. down, arm 31 2gis held'by. stop 3,20 and. the note is maintained: at constantvolume in. respect to,the con,- trol: by potentiometer 3114, although: the volume may be varied'by-other. means to be described below. When. the keyboard lever 30! is released sufficiently, contact 3.3.6 is disengaged, and sole-- noid 3221s; deenerg'ized.v This; allows contact 3M to complete its revolution. and decrease the intensity of. the electron beam in tube I50, to diminish the volume of, thenote according to the taper of the resistor 365 and. the. position, of. foot pedal 32 to provide the. desiredgdecay.

The volume. of; each, note may be controlled separately by, the pressure applied to the corresponding keyboard. lever. The amount of pressure applied to lever. 38:1. results in, more or less depression of the. lever against the tension of spring 382. The greater the depression of lever 3th, the more, resistors 30.5, are cut out, of, the dynamic potentiometer circuit resulting, in a greater amount of current flowing in the circuit and causing a greater. intensity. of the electron beam in. tube I50. anda greater volume of sound.

The function of switch. 390. which is. operated by keyboard lever; 301i; will be described; below with. respect to. Fig.v 9..

It will be understood that; it might. be desirable, in some music that; the duration of the decay; of.

a note extend until. a time after the finger has been lifted from. the keyboard lever. Furthermore thekeyboard levers 30;! could; be arranged with a slight. purposeful misalignment of key lever contact positions sothat. chords will automatically be played. with slightly different initiation times anddecay'periodsrin; order thata too.

mechanical eifectbe avoided.

A tremolo effect. may beproduced directly by rapidly varying the pressure on' each keyboard,

lever since volume is; a. function of; the amount by which the lever is pressed. However, a. more sustained effect may be. produced by the means shown in Figs. 2 and, 2a. A light source 58c; pro,- duces light which is directedinto. abeam 589: by optical element 58l. The light beam; 589. is focused by optical. element 582 on the cathode of photosensitive cell 583. Directly adjacent light beam 589 are a plurality of. reed elements 58 5. Each reed element 5814 as seen. in Fig. 2a consists of a thin reed 586. anchored at one end. to. the frame of the musical instrument. The other end carries an obturating means 58.8;- and handle means 581. Photocell 583; controls the grid of a tube in the amplification circuit.

In operation, when a sustained automatic tremolo effect is desired, the musician displaces one of reeds 584 by pressing and rapidly releasing handle 58?. The reed will then continue. to vibrate, alternately blocking, or partially block:- ing, light beam 589.from photocell583 and causing the volume, of the music to-vary rapidly in volume in accordance with the period of vibration of the reed caused. tooscillate. The reeds 584. are each of different length. or thickness so that each will vibrate at a different frequency.

The reedsmay'be made to vibrate, singly or in any desired combination. Electromagnetic driving means may be arranged for causing the reeds to continuously vibrate. This means for producing automatically a. tremolo; effect is pr f r bly placed closely behind the keyboard as shown in Fig. 2 for the; convenience of the musician. It will be obvious that such a tremolo producing means could be used with, each manual for individual: results; or even. with each harmonic of a note.

In. Fig. 8- isshown. oyer-all volume potentiometer. 252: also. shown. in Fig. 6. The adjustment of: potentiometer 252. iscontrolled by foot pedal 360, The position. of foot, pedal 360 therefore controls. the oven-all volume of the instrument.

There being a. dynamic potentiometer circuit corresponding: to the one. containing potentiometer 3M associated: throughswitch 348 with each contact l8! of tube I82, the action. of distributor tube I82 is tocause the electron beam of tube 158 to be modulated successively during small increments of; time in. accordance. with. the keyboard levers operated, the. proper attack or decay vol ume beingimpressed. on each note as it is sounded during its increment of? time.

Reference is now made more particularly to Fig. 9 for a, description of: a quality control circuit used in this invention. Tube [50, patterns |'5'61l.65, and compensating resistors 225 correspond: to those elements shown. in Fig. 6. Resistors 225are each connected. to a contact spring 315. Opposing contact springs 31.6 are connected tov ground. Between contacts 315 and 376 are intermediate contact. springs 37:1. each having fixed theretoa downwardly extending projection 318 of insulating material. Springs 37.! are normallyincontact with. springs 315. Intermediate springs 31! may each. be connected through switches 31.9: to harmonic attenuator resistors 26. Alternately switches 31!! may connect selected. harmonic patterns: to ground eliminating the harmonics soconnected.

Immediately above the top intermediate spring 311 is theend of a plunger 384fixed to the core of solenoid 385. The plunger 384 is biased upwardly by spring 386 and extends through dashpot 381 the action of which is regulated by handle 388. Solenoid 385 is connected in series with battery 392' through contact 3953v of keyboard lever 3.0L

When keyboard lever 3lll is depressed, it will be seen that. solenoid 385 will-be energized by the closing of contact, 3.9.0. Operation of solenoid 385 will urge shaft 384 downward against the tension. of spring 386. at a speed determined by dashpot 381 and the setting of regulating handle 388. As shaft 384 progresses downwardly, first spring 311, will. disengage spring 3%. and engage spring 37 5, thus. disconnecting fundamental pattern |56fromground and connecting it in the parallel. circuits of harmonic resistors and 226. or 226".

As shaft, 384. moves further down. the second spring 317 is moved to disconnect the second harmonic pattern I51. from. ground and connect it in the potentiometer circuit of resistors 225 or 2-28," associated with the second harmonic The remainingharmonics. are thus added to; audible note, in. rapid, succession.

Patterns l'5fi;-.|165 may be connected through resistors 225;, contactsprings 315-311 switches 3.19, through: harmonic attenuators 225and 225 connectediin. parallel, through battery 392 and the electron beam of tube 158 to form a complete potentiometer circuit. Sliding contacts 363 are fixed to rods 394 moved against a restraining spring, not shown, by floating bars which in turn are moved by cams 3S6. Cams 336 are mounted O11 shaft 391 which is turned by rack and pinion 398. The rack is fixed to stop 339.

Movement of stop 339 to various positions will be seen to suppress or accentuate the various harmonics as determined by the shapes of the cams 396. When resistors 226 control quality, there may be simulated quality within one tone classification, i. e., Woodwinds, while movement of stop 399 may produce variation within that classification, such as oboe, clarinet, etc.

Each resistor 22%) is mounted on a resistor support 462 which is slidable with respect to contact 393 as determined by the position of stop #383. A spring tensioned ball 464 fitting in a notch on shaft 435 of stop 403 allows the operator of the instrument to know by touch w 1611 he stop is in its normal position. Stops 433 allow each harmonic to be separately adjusted.

Alternate harmonic attenuator resistors 226 have contacts 333' moved by shafts 384. Shafts 3% are moved by fioating bars 395' against restraining springs, not shown, which are in turn moved by cams 3913'. Each cam 395 is rotated by a shaft 351 and each shaft 351' is rotated by a separate knob 408. Thus the attenuation of each harmonic may be pre-adjusted or preset to a degree, before starting a rendition chosen by the musician. Cams 236' aid in keeping contact 333 contact 393 to have a different motion from that of knobs 438.

A third set of alternate harmonic resistors 225" are provided. These resistors are for independent separate harmonic control and are connected to stops in the form of calibrated sliding handles or to levers for rapid manipulation. They are not intended for group action. Resistors 225 are always connected and are intended for rapid manipulation to achieve variations in the quality already set in the instrument by the musician.

Switch 4H1, at the operation of the musician, selectively connects the contacts of the potentiometers containing resistors 225, or 226' to the pulse integrator and thus causes the notes sounded to be in accordance with the harmonic attenuation determined by the harmonic-attenuator group selected. It will be understood that there would be a number of sets of resistors such as 225 representing tone families such as the oboe, clarinet, etc., and that there could be a number of sets of resistors such as 226' at the command of the musician.

Switch 419 includes curved clamps 4!! having opposed concave curves, said clamps being urged together under tension to have opposite parallel motion when forcibly separated. Buttons 412 are urged upwardly by springs M3 and have lower bulbous portions 414 adapted to be squeezed between clamps 41!. As one button 412 is pressed down and the associated bulbous portion 414 squeezes clamps 4H apart, the bulbous portion already between clamps 4!] will escape, forced up by its spring 4l3. Switch 419 operates to connect one set of contacts 393 or 393 to the pulse integrator and thus allows selection by the musician of the type of quality control used. This selector device would also be adaptable for use with dynamic selector switch at the selected position and allow the stop 343 of Fig. 7. Switches such as 390 are operated by other keyboard levers.

In Fig. 10 is shown an alternate form of quality control employing capacity attenuation. As explained by Figs. 5a-5f, the beam current is in the form of high frequency pulses which may be attenuated by capacitance. In Fig. 10 patterns such as I56 are each connected to a resistor 221, all of which are connected through overall attenuation condenser 42!, coupling circuit pulse integrator, detector 420 and amplifier 231, these elements being similar in function to elements I28, I29, 135 and 136 of Fig. 4, and loud speaker 216. Voltage is applied between anode patterns 58 and cathode of the cathode ray tube by battery 422. The various attenuating bleeder circuits, condensers 42I, 423, 425 and 425' discharge between pulses except 42l, which discharges directly, through resistors 221 and battery 422 to cathode. Other types of impedance, either variable resistors or inductors, may replace the condensers shown here.

In the modification of Fig. 10, frequency C0111- pensation for the natural characteristics of the ear is accomplished by condensers 423 which vary the voltage at the junctions of the patterns such as I56 and resistors 221.

In parallel with condensers 423 are harmonicattenuator condensers 425, one condenser 425 being connected between each pattern, such as l56 and the electron beam potential supply. Condensers 425 provide tone families similar in function to stop 399 of Fig. 9 and 425 for use similar to stop 408 or resistors 225' (Fig. 9) that is for preset qualities or independent control. Switches 424 permit alternate selection of the system including condensers 425 or the system including condensers 425'. Condensers 425 comprise a relatively movable plate, or plates, 425 and a relatively fixed plate, or plates, 421. Movable plates 426 are shown to be mounted on shaft 434 for rotation. Shaft 434 has mounted thereon a pinion 43| which is rotated by oppositely acting stops 429 and 430 each of which carries a rack meshing with an opposite side of pinion 431. Plates 426 can therefore be rotated to any desired degree by pushing one or the other of stops 429-430. Plates 426 and 421 are shaped to attenuate the various harmonics to achieve the sound effects desired for the various settings of stops 429-430.

Relatively fixed plates 421 may also be separately rotated with respect to plates 423 by stops 423 carrying racks meshing with pinions fixed to plates 421. Stops 428 allow individual adjustment of the attenuation of the various harmonics within the tone family compass as desired by the musician.

In Fig. 11 is shown an alternative distributorswitch arrangement in which a plurality of gas filled tubes such as tubes 435, 436, 431 and 438, each have an anode, control grid, and cathode. Each of the cathodes of tubes 435-438 is connected to a common junction point 445 through a variable cathode resistor 440 and potentiometer 44!. The anodes of tubes 435-438 are connected together through conductor 446 and to the oathode through common junction point 445 and battery 441. Cathodes of adjacent tubes 435-438 in the ring-like series are connected through condensers 442. The grid of each tube 435-438 is connected to the cathode of the preceding tube in the series by resistors 448 and 449, and battery 450. Voltage taps on potentiometers 4 are connected to the grid of pentode 60 which corresponds to pentode 6D in Fig. 6. Switches 439 21 between the taps on. potentiometers. 4:41. and the grid of tube 50 constitute keyboard lever switches corresponding to 300 and 300' of Fig. 7:.

Relaxation generator 452. of conventional. constructiongenerates a successionof positive pulsesv of steep wave front at supersonic distributor, frequency. The interval betweenpulses is the increment of time during which. one. note will be sounded until it is reached again by operation of the distributor circuit. The pulses generated by oscillator 452 are applied to the grids of tubes 435-438 through condensers 453. It will be understood that in the. actual circuit used. there will be thirteen gaseous, triodes such. as. tubes. 4351-438, one corresponding to. each of the electrodes 181 in tube 182. of Fig. 7..

In explaining the operation of the circuit of Fig. 11, it will be assumedthat tube 355 is conducting.

the cathode of that tube and hence the. negative bias on the grid of tube 43.6 islowered because of the connection through. resistors 4:48: andv 449.

and battery 45.0 to resistor 4.40; Batteries. such as 450 are for thepurpose of maintaining a. negative, bias on the grids of. tubes 4 35-438. When the next, positive pulse from relaxation oscillator 452 is applied to all the grids of tubes. 435-438, tube 436 will begin to conduct since it has asufficiently low grid bias. Tubes 431 and 438 do not have a sufficiently low grid bias to. be rendered conducting by the pulse.

the condenser betweenthe cathodes of. tubes 435 and 436, making the cathode of tube 4.35.so positive that the tube stops conducting. On arrival of the next pulse from oscillator 452Jtube4'31 will begin to conduct and tube 436.- will be cutoff. This process is continuously. repeated, each pulse from oscillator 452: causing the next tubeto conduct and the tube presently conducting to be cut off. Similar circuits employing vacuum tubesare Since tube 435 is conducting, current. is flowing through resistor 440 connected. with.

Whentube 436 begins. to conduct the drop across its resistor441lcharges known to the art and may be employed, in place of the gas filled tube circuit shown.

Reference is now made more particularly to Figs. 12 and; 13 for a; description of anembodiment of this. invention using. continuous harmonic patterns. In this embodiment cathode ray tube 490 which includes horizontal and vertical deflection plates 491., and 492, respectively, carries on its end wall 493 and. concentrictherewith a plurality of ring-like, substantially flat, continuous patterns- 494, the radial dimensions of which vary in sinusoidal manner. The inner.- most of patterns 494 varies in radialdimension as a single complete sine wave. The adjacent pattern varies to form two completesine waves-and the succeeding patterns similarly form. the successively higher harmonics.

Patterns 494 are. each connected to the harmonic compensation and attenuation circuit 498 which is in turn connected through pulse integrator circuit 231, detector 244 andamplifier 26.1lto speaker 216. Harmonic compensation, and attenuation circuit 498 containscompensation and attenuation resistors 2,25 and ZZGshoWninFig. 6. Circuits 231, 244, and 25,0, and. speaker. 2716*have a similar construction and operation to.that of the same numbered-circuits in Fig. 6. Frequency control circuit 501 contains tubev 611. and its associated circuit shown in Figs. 1 and 6. Distributor 5112 contains an electronic distributor tube similar to tube 182'ofFig. 6. Keyboard 500 is interconnected with frequency control circuit 501 and distributor, circuit: 502', so-that there is produced in the output of: frequency control circuit 5311 a voltage having a magnitude indicative of the pitchof the note being'played on keyboard 59B. and sounded at that incrementof time. Distributor 502 operates to cause the output voltage of frequency control. circuit 501 tov successively represent over small increments of time the variousnotes played on keyboard 500.

Sine wave oscillator 5.03. produces. a sine wave of a frequency controlled by the output voltage of frequency control 501.. Such. circuits for modulating frequency are well known. The sine wave produced by circuit 51l3.is split into two sine waves degrees apart. in phase buteach having the frequency of. the original sine wave. The splitting of. the output of circuit. 503 is accomplished by the circuit including condenser 505 and resistor 5116. One of the quatrature sine waves is applied tov horizontal sweep. circuit 501 through transformer 5118 while the other quadrature sine wave is applied to vertical. sweeplcircuit 5139 through transformer I 10'. Vertical and horizontal weep circuits501 and 599 are modulator circuits which modulate the amplitude of the voltages applied. to the input circuits thereof. This amplitude modulation is controlledv by sawtooth oscillator 515 which is a circuit capable of generating a saw-tooth wave having a frequency relatively highcompared to the frequency of sine wave oscillator 503.. The, saw-tooth wave produced by oscillator,515.isapplied.to sweepcircuits 5il1;and 5119 to modulate in, amplitude the quadrature wavesfrom circuit. 50.5.and 596. The deflection waves produced by'horizontalsweep circuit 501 and vertical sweep circuit 5.119: are applied to horizontal deflection. plates 491 and vertical defiection plates 492, re pectively, of tube 493;

Saw-tooth oscillator 515. is connected. topulse integrator 231 through peaker circuit 5 lfi'which is constructed similarly to peaker circuit 245. in Fig. 6 and operates to. derive a pulse from the radial return deflection voltage of the saw-tooth-wave developed by circuit 515.. The pulse frompeaker 516 trips integrator 231,. discharging the condenser therein as explainediabove.

In the operation; of the embodiment of. the invention shown in Fig. 12., keyboard 5110, distributor 502, and frequency. control circuit 5111 act to produce a series, of voltages, each representing the pitch of the keyboard lever depressed and each lasting over an incrementv in a supersonic distribution period as explained above. Each short voltage level. frequency modulates sine wave oscillator. 503.: to produce a sine wave having a frequency indicative of the pitch of the keyboard lever producing said voltage level.

The two quadrature voltages produced by circuit 505--506, having a frequency as produced by sine wave oscillator 563; cause the pencil beam produced by tube 490 todescribe a circular trace on the end wall 493. Saw-tooth oscillator 515 modulates the amplitude of the vertical deflection voltage causing the circular trace on end wall 49.3.. to be contracted and expanded overthe patterns 494 at a highrate of speed. This results in arapid radial scan which-moves circumferentiallyover patterns494 at a rate determined by the note played on keyboard 500that momentarily is being sounded by the instrument through the action-of. distributor 5112.

The signal produced by patterns 493 passes through circuits 498, 231i 244, and 260 where it is. handled in. the-same manneras described in Fig; 6'. integrator-23.1: and add the signals produced in Peaker 51.6. operates to trip pulse 

